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Sanding is the most commonly used cultural practice in cranberry production in Massachusetts. Growers apply a thin (1/2 to 2 inch) layer of sand on the surface of producing cranberry bogs at 2 to 5 year intervals in order to promote growth, improve productivity, suppress disease, and reduce insect populations. Sanding, as a pruning mechanism, is particularly well suited to the cranberry system: runners are anchored and bare wood, at the base of uprights, is covered thus promoting rooting and the production of upright stems (the portion of the plant that bears the crop). Mechanical pruning can be less than optimum due to the trailing nature of the cranberry growth habit and removal of flower buds (upright tips) during such pruning.
Sanding covers the leaf litter (‘trash’) layer on the floor of the cranberry bog. This has several benefits, including stimulation of organic matter decomposition (nitrogen release and relief of root congestion), suppression of fruit rot fungus inoculum, and limitation of the habitat of cranberry girdler larvae which feed on the area of the stem that is covered by the leaf litter layer. Sanding improves soil drainage and can physically strengthen peat soils so that mechanical operations on the bog are easier. The sand layer reduces moisture in the upper layer of the soil leading to accelerated warming in the spring and increased release of nitrogen from organic matter in the soil. This increases the potential for growth and productivity without additional fertilizer input. Development of the plants may also be accelerated, so frost hardiness may be lost earlier in the spring. Sand absorbs and releases more heat than the organic layer that it covers so that frost danger is less on sanded bogs (temperatures remain 2-3o F higher on freshly sanded bogs if sand is moist).
By choosing sanding instead of mechanical pruning, growers gain the benefits of insect and disease suppression, improved drainage, better root growth, and some frost protection. This can lead to lower pesticide, fertilizer, and water (frost protection) requirements.
Sanding can be accomplished by several different methods. Those commonly used include sanding on ice, sanding in water (barge sanding), or applying dry sand directly to the vines using ground rigs run directly on the vines or on rails (rail sanding). When choosing a method, growers should weigh several factors, including the following. Ice may not be available when a bog needs sanding. Barge sanding may not anchor runners well (less pruning benefits). Sanding on the vines (dry sanding) is the most likely to be associated with vine injury even if the sanding is done when the vines are dormant. Recent developments in the use of rail sanding may lessen the impact of dry sanding. Sanding is considered important enough that even damaging methods are preferable to no sanding for many growers.